PS: I read your other post also, in which you have written that in a
simulation you added 2000+ users. Can you please tell me how did you
add the users, is it done on 'one by one' basis or is there any way
to add existing users in a group?

I am sorry, I am very new to LDAP so I cannot help you but can seek
your valuable advise...

I'm not quite sure what post you are referring to, but I've tested OpenLDAP
with many different numbers of users, and my production servers at Stanford
hold almost 400,000. I always use slapadd to bulk load my database, with
the "-q" flag, since I know the structure of my data is correct.